This invention relates to a filter press of the type having filter plates mutually locked to each other and individually and consecutively slidable after release of the locking means therefor so that upon closing the filter press each filter plate is locked to the filter plate following it by a locking hook engaging behind a locking bolt and a blocking element positively blocks the unlocking movement of each filter plate until the filter press is opened whereupon the filter plate is then separable from the following filter plate by means of a transport element moving along the filter plate only after the locking hook is released by the blocking element.
A filter press of this type is disclosed in German Offenlegungsschrift No. 25 04 602. In this prior art filter press, the blocking element which assures the locking between two adjacent filter plates is mounted on a third filter plate preceding them in the opening sequence. When this filter plate carrying the blocking element is removed by the transport element during the opening of the plate, the locking means between the two following filter plates is therefore released, so that at the next stroke of the transport element the forwardmost of these two filter plates can be engaged by the transport element and moved along. However, this means that after the separation of a filter plate carrying the blocking element, the two next filter plates are no longer locked positively together during the interval of time until the next stroke of the transport element. That is, at most, the next two filter plates are frictionally locked to each other if the lock means consists of a spring-loaded lock. It has been discovered that this frictional anchorage is not sufficient in many cases, particularly in the case of strongly expanding filter cakes, such as cakes formed from carbon sludges wherein the foremost filter plate of such next two filter plates can separate accidentally from the as yet unopened stack of plates and enter an intermediate position. Accordingly, during the next stroke of the transport element, this filter plate now following is taken along by the transport element, and can strike the filter plate which had previously moved into the intermediate position, which may lead to service breakdowns and damage.
Similar problems may also occur with a filter press as shown in U.S. Pat. No. 3,563,386, in which, at the separation of a filter plate, the locking between the two next filter plates is simultaneously totally released. When this takes place, the foremost plate of the as yet unopened stack of plates has no anchorage at all to the stack of plates during the time it waits for the return of the transport element, and can very easily become detached from the stack.